Code: Select all
\documentclass[fleqn]{article}
\usepackage{amsmath}
\usepackage[shortlabels,inline]{enumitem}
\usepackage[version=3]{mhchem}
\usepackage{pifont}
\setlength{\parindent}{0in}
\setlength{\parskip}{0in}
\setlength{\mathindent}{0in}
\newlist{longenum}{enumerate}{6}
\setlist[longenum,1]{label=\arabic*.}
\setlist[longenum,2]{label=\alph*)}
\setlist[longenum,3]{label=\alph*)}
\setlist[longenum,4]{label=(\roman*)}
\setlist[longenum,5]{label=(\alph*)}
\setlist[longenum,6]{label=\roman*)}
\begin{document}
\begin{longenum}[nosep,leftmargin=0in]
\item Hello \\
\begin{array}[t]{@{}ll@{}}
\begin{minipage}[t]{2cm}$\left(-1\right)\times$\begin{longenum}[leftmargin=0in]\item[\ding{192}] \ce{H2O}\end{longenum}\end{minipage}
\end{array}
\end{longenum}
\end{document}